The Syrian government has agreed to allow UN inspectors to investigate allegations of a suspected chemical weapon attack near Damascus.

The team is to begin work on Monday. Activists say Syrian forces killed more than 300 people in several suburbs east and west of the capital on Wednesday.

UK Foreign Secretary William Hague warned that evidence could have been tampered with, degraded or destroyed in the five days since the attack.

Syria has blamed "terrorists".

State media reported that chemical agents were found in tunnels used by rebel fighters, and also that soldiers suffered "suffocation" in fighting around the suburb of Jobar.

State TV is meanwhile reporting that the governor of the central district of Hama, Anas Abdul-Razzaq Naem, has been killed in a car bomb attack.

'Degradation of evidence'

Media captionWilliam Hague said it was 'clear' the Syrian regime was behind the attack

The Syrian foreign ministry statement broadcast on state television said an agreement to allow UN chemical weapons experts to "investigate allegations of chemical weapons use in Damascus province" had been concluded on Sunday with the UN's disarmament chief, Angela Kane.

The agreement was "effective immediately", the statement added.

A spokesperson for UN Secretary General Ban Ki-moon subsequently announced that the inspectors were "preparing to conduct on-site fact-finding activities", starting on Monday. A ceasefire will be observed at the affected locations, the statement said.

Analysis

By Yolande KnellBBC News, Beirut

It was last Wednesday that amateur videos of Syrian children choking and fighting for their lives and young men suffering horrible convulsions first caused international outrage.

Western countries expressed deep frustration that, although UN chemical weapons inspectors were staying in Damascus at the time, they were not able to go immediately to the city's eastern suburbs to investigate what happened.

It appears that pressure from Syria's allies in Moscow and Tehran may now have helped persuade the authorities to allow access for the experts.

They are due to head to the affected sites on Monday. The Syrian military and opposition fighters are expected to cease hostilities in the area.

The work of the UN team is likely to involve taking soil, blood, urine and tissue samples for laboratory testing to see if banned chemical agents were used. There are concerns that evidence might already have degraded or been destroyed by recent intense shelling.

Russia, a key ally of Syria, welcomed the decision to allow the inspectors in but warned the West against pre-empting the results.

Mr Hague, though, said time was running out for the inspectors' work.

"Much of the evidence could have been destroyed by... artillery bombardment; other evidence could have become degraded over the last few days, and other evidence could have been tampered with," he said.

Medecins Sans Frontieres (MSF) said on Saturday that three hospitals it supports in the Damascus area had treated about 3,600 patients with "neurotoxic symptoms" early on Wednesday morning, of whom 355 died.

While MSF said it could not "scientifically confirm" the use of chemical weapons, staff at the hospitals described a large number of patients arriving in the space of less than three hours with symptoms including convulsions, pinpoint pupils and breathing problems.

UK Prime Minister David Cameron has discussed the situation in a telephone call with President Francois Hollande of France.

"They agreed that a chemical weapons attack against the Syrian people on the scale that was emerging demanded a firm response from the international community," a Downing Street spokesman said.

"This crime must not be swept under the carpet."

Mr Cameron agreed a similar response in a telephone conversation with US President Barack Obama on Saturday evening.

'Red line'

Later, Syria's Information Minister, Omran Zoabi, warned that US military action in Syria would not be a "walk in the park".

"If the US leads a military intervention, this will have dangerous consequences. It will bring chaos and the region will burn," he said.

A year ago, President Obama said that any attempt by Syria to use its chemical weapons would be a "red line" for the US, and change his administration's "calculus" in the region.